As someone who programmed in "classic C++" for decades, I feel like modern C++ is pretty different, and that it's not just syntactic sugar to make some ugly things easier. The biggest example is that my natural inclination to use raw pointers everywhere and manage all memory myself, while idiomatic modern C++ is full of unique_ptrs and shared_ptrs everywhere, and raw pointers seem to be regarded as a code smell. Converting to this style is not an automatic process.

For people who are coming from a classic C++ background, I find Bancila's Modern C++ Programming Cookbook to be a good first stop for discovering modern C++ idioms.